Unibody construction has become standard for most U.S. non-commercial road automobiles, especially those of the compact and smaller sizes. Such unibody construction employs shorter side rails for a frame which is largely made up of formed steel sheet metal stampings welded together.
Automobile bumper systems in present commercial use employ a bumper member, normally a steel stamping, mounted to a pair of spaced-apart rods which form part of a shock absorber mounting. These bumpers are designed to take a straight-on hit and to absorb a good part of the energy in shock-absorbing members. Unfortunately, they do not perform as well when oblique hits occur.
The primary support for this type of member is the shock absorber structures which project inwardly from the bumper and are secured at their bases to the body of the automobile. These are essentially horizontal cantilever supports projecting to form with the bumper a unbraced "box" or rectangular structure.
Thus, oblique forces acting on the bumper tend to bend the shock-absorbing members sideways and shift the bumper sideways into the unibody and the "skin" sheet metal. Even a relatively minor hit can thus result in a major repair job and major repair bill to the owner.
Also in certain accidents, e.g., those involving a large-tired vehicle and a conventional automobile, the cantilevered bumper system serves as a stairstep or ramp over which the large wheels can travel and thus reach the passenger compartment easier and quicker.
Such commercial bumper systems are also expensive to install requiring a number of separate, labor-intensive steps to mount the shock-absorbing structures to the body and attach the bumper unit to them.
Pressurized bumpers have been produced for many years on conventional automobiles (see, for example, U.S. Pat. Nos. 2,089,500; 2,202,460; 2,236,507; 3,829,141; 4,061,385) and have and have been proposed to be used with the dual shock-absorbing system (U.S. Pat. No. 3,961,818), but they have not met with widespread commercial acceptance and do not overcome the aforementioned problems.